Solar-Powered Phone Charger

For my backpack I want a solar panel charger that folds up small enough to clip on. Pulling energy from the sun while I walk to class feels like something that should have been normal 10 years ago. Panels I've been looking at weigh about 14 ounces and charge a phone in roughly 3 hours of direct sunlight, slower than a wall outlet but perfectly fine for a day outdoors. Converting something abundant and free into something I currently pay for is a trade I like.